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The invention described in this patent was made by an employee of the United States Government and may be manufactured and used by or for the Government for governmental purposes without the payment of any royalties.
1. Field of the Invention
This invention relates to a coaxial valve which is especially suited for use in propulsion in aircraft and spacecraft for the control of flow of liquids and gases under conditions wherein solenoids are not as effective.
2. Background of the Invention
The most significant use for coaxial valves is in their high flow capability and pressure balanced control element. This means that hydraulic forces against the control element remain balanced in both open and closed positions and the transition between, allowing smooth, controlled, predictable and fast actuation speeds. The valves operate by urging against a valve seat a cylinder through which the working medium flows.
Coaxial valves are commercially available, but such valves are actuated by electromagnetic coils, compressed air, helium under pressure, or hydraulic fluids. Since coaxial valves usually contain only one moving part it has not been easy to provide for electric motor actuation. These difficulties will be apparent from a reading of a Martin Roth et al Application 20010011715 published in the United States. The valve described is a coaxial valve including a housing with an inlet and an outlet connected by a flow passage, along with a valve sleeve arranged in that flow passage. The actuating drive is a servomotor which is fixed to the valve housing. A recirculating ball nut assembly or a planetary ball nut assembly is used to translate the rotary movement of the servomotor to a back-and-forth linear movement. A transmission part then transmits the linear movement of the actuator to the valve sleeve. This transmission part is in the form of an adjusting lever. The adjusting lever is a rocking lever having one end coupled to the actuator, its other end coupled to the valve housing, and its center portion coupled to the valve sleeve. Considering the number of additional components, and bearings which are included for efficient operation, it can be seen that the use of a motor in conjunction with a coaxial valve is not without its drawbacks.
European Patent Application Publication EP-OS 0 257 906 referred to in the published Roth et al application discloses an axially-movable seat body driven by an electric motor. In this arrangement a spindle/nut is used. To operate the valve the rotor of the electric motor largely makes use of the cross section of the flow channel. But to do so the rotor itself is located in the flow stream of the conveying medium. It is pointed out in U.S. Application 20010011715 that such an arrangement is associated with several disadvantages. The units (bearing, rotor, gearing) which are incorporated directly in the flow channel, impair the flow, so that considerable losses in pressure have to be anticipated. Accordingly it is understandable that many valves being proposed or considered involve designs and systems which sometimes lead to bulky packages because of their mechanical features. It is suggested, then, that there is still a need for a motor driven coaxial valve. Such a valve is provided herein.
As can be discerned from the prior art one of the challenges facing those improving coaxial valves is the requirement for suitable linear actuation.
An object of this invention is the provision of a linear actuator which is much less complex than those now in use.
Another object of the invention is to improve a coaxial valve for controlling a flow of a liquid or gaseous flow medium therethrough.
The valve herein includes a valve housing with an inlet, an outlet, and a flow channel passing in a longitudinal direction therethrough from the inlet to the outlet. Arranged in the flow channel is a closing body provided with a valve seat. In alignment with the closing body is a ball screw actuator which includes a ball nut and a cylindrical screw. The ball nut surrounds a threaded portion of the cylindrical screw. The cylindrical screw is provided with a passageway therethrough forming a cylinder through which fluid flows. The cylindrical screw is disposed in the flow channel to become a control tube allowing the flow medium to flow therethrough. The control tube is adapted to move in the longitudinal direction toward and away from the valve seat of the closing body when rotated through its ball bearings by the ball nut. One end of the control tube is adapted to abut the valve seat of the closing body when so moved. To rotate the ball nut an actuating drive is employed. This actuator is adapted to be driven by a stepper motor so that the nut rotates to advance the control tube to a closed position in which the control tube end contacts and seals against the valve seat of the closing body to close the flow channel. In addition, the nut can advance the control tube to an open position in which the control tube end is spaced a distance apart from the closing body to provide an opening between the control tube end and the closing body to allow the flow medium to flow through the control tube and through the valve housing outlet.
For future space launch vehicles the use of electro-mechanically actuated valves are being proposed for controlling the flow of propellants to rocket engines. The most notable advantages of using such valves over traditional pneumatically or hydraulically actuated valves are the elimination of associated reservoirs, tanks, lines, fittings, solenoid valves, and the ability to drive multiple engine valves through a single electric engine controller. Electro-mechanically actuated valves offer precision control of valve positions. There is also a potential for reduced ground operations ,improved reliability and safety, and fast vehicle turn-around times. This invention eliminates extra mechanical features such as levers by combining the function of a valve sleeve or control tube with that of a linear actuator. Position accuracy is also increased because the motor is more directly coupled to the control tube. In one embodiment the actuator drive includes a stepper motor and a ball nut retainer. The ball nut is keyed to a ball nut retainer so that the nut rotates with the ball nut retainer to advance the control tube. Equally important, loads from the motor drive as well as hydraulic loads on the control tube are transmitted through a coupling nut along the entire circumferential area of the outer screw of the control tube rather than on two sides of the control tube as in the prior art. This reduces the potential for jamming. These and other features of the coaxial valve of this invention will become apparent from a description of the valve in conjunction with the accompanying drawings.